The invention relates to a process for controlling the speed of a vehicle travelling on a slope by means of active braking intervention.
Road vehicles having systems that maintain the vehicle at a constant speed as it travels on a gradient by automatically applying the brakes ("active braking") are known. Such vehicles are, as a rule, equipped with an anti-locking brake system (ABS), as well as with an automatic slip control (ASR). The components of the ABS and ASR systems, such as the electronic control units, wheel speed sensors, solenoid regulating valves, etc., are used to effect the abovementioned speed regulation on a gradient. Using the known devices, the driver is relieved from having to actuate the brake pedal constantly when the vehicle is travelling on a gradient. Even with a changing incline, uniform speed is maintained.
In DE-A-24 19 242, an electro-pneumatic brake force control circuit is disclosed that maintains a constant vehicle speed as the vehicle travels on a gradient through active braking so long as neither the gas pedal nor the brake pedal is actuated. The speed regulation on a gradient is switched off immediately when either the brake pedal or the gas pedal is actuated, or as soon as the superimposed ABS becomes activated.
Equipping a vehicle with a "hill descent control" mode (referred to hereinafter as "HDC") is also known from International Patent Application WO 96/11826 A1. This type of speed regulation on a gradient can be switched on manually by the driver with the activation of a switch. This type of regulation is able to maintain the vehicle at a constant low speed on a steep slope by means of active regulated braking of the vehicle without the driver having to actuate the brake. This system is particularly suitable for off-road vehicles driving on a slope that is steep so that the engine braking effect is no longer sufficient to decelerate the vehicle, even when the vehicle is in the lowest gear.
It is the object of the present invention to provide a process for controlling the speed of a vehicle travelling on a slope whereby the transition between normal driving and the state with active braking state is rendered particularly comfortable.